CoSi2 nanohexagons buried in silicon substrates. Effects of orientation of the Si host and kinetics of formation

G. KELLERMANN; L.G. MONTORO; P.C. DOS SANTOS CLARO; L.J. GIOVANETTI; L. ZHANG; F.G. REQUEJO; A.J. RAMIREZ; A.F. CRAIEVICH

Cordoba

Congreso; I Reunión Latinoamericana de Cristalografía y IX Reunión Anual de la Asociación Argentina de Cristalografía; 2013

Asociación Argentina de Cristalografía

We have previously described a simple method for obtaining thin hexagonal CoSi2 nanoplates buried in Si host single crystals. In this procedure a flat Si(001) wafer is covered with a Co-doped SiO2 thin film and then subjected to a high temperature isothermal annealing [1]. We demonstrated that Co atoms initially embedded in the SiO2 thin film diffuse into the Si crystal and lead to the formation of buried CoSi2 nanoplates. The thin CoSi2 nanoplates exhibit a hexagonal lateral shape and are parallel to and coherent with the {111] planes of the host crystal. We have performed additional studies of the same process using Si substrates with three different orientations of their external surface, namely Si(001), Si(011) and Si(111), in which similar Co-doped SiO2 thin films were deposited. Our TEM results showed that CoSi2 platelets with similar features are formed in Si(001), Si(011) and Si(111) substrates subjected to equivalent thermal annealing. Regardless the Si surface orientation, the lattices of the hexagonal CoSi2 nanoplates are coherent with and parallel to crystallographic planes of the {111} form. Our GISAXS results demonstrated that the sizes of the CoSi2 nanohexagons are functions of the crystallographic orientation of the external surface of the Si substrate. The thickness of the platelets varies for different Si substrate orientations from 2.8nm for Si(001) up to 5.7 nm for Si(111). Finally, in situ GISAXS measurements - at high temperatures - allowed us to determine the time dependence of the number density of CoSi2 platelets. Our results also indicate that the rate of growth of the CoSi2 nanoplates is, in all cases, a fast process that quickly leads to platelets with nearly constant final sizes. Work supported by LNLS, LME-LNNano, CNPq and FAPESP, Brazil; ANPCYT and CONICET, Argentina. [1] Kellermann G. et al, Appl. Phys. Lett. Vol.100 (2012) 063116.